Answer: In the first paragraph, the narraraor seeks to establish his credibility, as if he expects the reader to believe that his especially acute sense of hearing makes him more believable than an ordinary observer. The narrarator purports that his calm, detailed account will be accepted as truthful, despite some irrational decisions and actions. The narrarator's attention to detail clues the reader to "expect the unexpected" in terms of details the narrator's heightened senses reveal.
In the third paragraph, the narrator reveals that he has, in fact, killed the old man. We are hearing the account of a murderer rationalizing his actions, as if this is what anyone with his keen perception and ability to carry out this elelaborate scheme would have done. The reader realizes that this narrator is crazy, but we are still listening, but we can intrpret his intentions as absolutely irrational. Speaking corageously to the man by day, sneaking stealthily into his bedroom by night.
The fourth paragraph confirms the reader's suspicions that the narator is beyond belief: feeling the extent of his own powers. And even when he thinks the old man may have heard him, he persists in his incredibly slow, deliberate intention to intrude into the man's bedroom-- hoping to see what he has defined as Evil Eye-- as if the narrator has a duty to eliminate something that vexes only him. Our impression must be that this narrator can't escape the consequences of his actions.
